1. Field of the Invention
The invention relates to a frictional hinge device which is used to pivotably support a lid plate and a display of a portable business device such as a laptop note type personal computer, and particularly concerns to a frictional hinge device used to hold the lid plate and the display at a desired angular position by friction.
2. Description of Prior Art
This type of the frictional hinge device has been known as a torque damper which regulates a frictional torque to support a lid plate at the desired angular position. Examples are as follows:
(a) A metal plate (in the form of disc) is provided in a slit defined on a metal casing so that the metal plate can rotate in unison with a shaft. The metal plate is always urged by means of a spring washer.
(b) A rotary shaft is supported by a metal plate with a stay member engaged against one end of the metal plate. The torque damper utilizes a surface friction between the stay member and the metal plate.
(c) A shaft is rotatably supported by a taper bearing in such a manner that the shaft is urged against a tapered surface of the bearing by means of a helical spring or a dish spring.
(d) A rotary shaft is directly clamped by a metal holder to provide a surface friction between the rotary shaft and the metal holder.
On the other hand, a shaft lock device is disclosed by Laid-open Japanese Patent Application No. 7-26825 (laid-open on Jan. 27, 1995, assigned to Kabushiki Kaisha Kato Manufacturing Factory). This teaches that an outer shaft is made of a synthetic resin and integrally molded with an inner shaft. Due to a surface friction resistance caused from a thermal expansional difference between the inner and outer shafts, it is possible to hold the inner shaft at the desired angular position while permitting the inner shaft to pivot relative to the outer shaft against the surface friction resistance therebetween. This torque holds a display of a note type personal computer at the desired angular position.
In the frictional torque dampers (a) and (b), these however increase the number of components parts. Additionally, these dampers necessitate to diametrically enlarge the metal plate, which hampers to make them compact and less costly. In order to adjust the friction, it is necessary to alter a caulking degree of the metal plate against the shaft. This is a time-consuming procedure.
In the frictional torque damper (c), the urging force of the helical spring is altered by a threaded portion and nut when adjusting the surface friction on the tapered surface. This inconveniently requires a time-consuming operation.
In the frictional torque damper (d), the surface friction is insufficient to maintain a stable torque for an extended period of time.
In the shaft lock device disclosed by the Laid-open Japanese Patent Application No. 7-26825, a surface roughness, surface treatment and frictional coefficient are suggested as means to determine the torque between the inner and outer shafts together with their diametrical dimensions.
However, this disclosure remains silent about qualitative and quantitative analyses on the relationship between the inner and outer shafts. This causes no smaller variations on the torque when the inner shaft pivotally moves. This also causes abnormal noise due to a stickslip phenomenon when pivotally moving the inner shaft while losing a good endurance with a frictional torque reduced due to an unacceptable amount of wear between the inner and outer shafts.
When using the surface friction between metallic members, grease is required for lubrication. The grease becomes a likely cause for environmental pollution.
Therefore, the present invention has been made with the above drawbacks in mind, it is a main object of the invention to provide a frictional hinge device which is inexpensive with no fear for environmental pollution and no abnormal noise due to a stickslip phenomenon with the least torque variations and is capable of maintaining a stable surface friction resistance between a shaft member and a support member for an extended period of time so as to hold the support member at the desired angular position based on the surface friction resistance.
With a frictional hinge device having a support member rotatably supported by a metallic shaft member, a shape factor (W) in relation to the metallic shaft member and the support member is defined as 1.5xe2x89xa6Wxe2x89xa63.5.
This secures a relatively larger torque/volume efficiency and torque holding rate in which the support member tightly engages with the metallic shaft member to provide a good surface friction resistance therebetween. When the support member is subjected to a frictional torque greater than the surface friction resistance, the support member pivots around the metallic shaft member relatively. When the support member is subjected to a frictional torque less than the surface friction resistance, the support member stays to be held at an appropriate angular position by the surface friction resistance.
With the shape factor (W) in relation to the metallic shaft member and the support member defined as 1.5xe2x89xa6W xe2x89xa63.5, this increases the torque accumulated per a unit volume to enhance the torque/volume efficiency with a greater torque holding rate, and thereby significantly reduces torque variations and a stickslip phenomenon with no abnormal noise due to the stickslip phenomenon when the support member pivots in relative to the metallic shaft member. This enables to readily predetermine a required quantity of the surface friction resistance to hold the support member at the desired angular position.
With the surface friction resistance equivalent to a total frictional length between the support member and the metallic shaft member, it is possible to cope with an increased frictional torque between the support member and the metallic shaft member by combining a plurality of the same frictional hinge devices. This eliminates the necessity of discretely manufacturing a longer frictional hinge device. This is advantageous in cost.
In addition to the shape factor (W) defined as 1.5 xe2x89xa6Wxe2x89xa63.5, the support member is formed by a synthetic resin. This enables to tightly engage the synthetic resin with the metallic shaft member due to the surface friction resistance between the different materials.
With the support member molded by a synthetic resin around the metallic shaft member tightly by injecting the synthetic resin into a heated mold in which the metallic shaft is placed in advance, the support member tightly engages with the metallic shaft member due to a residual stress appeared between the support member and the metallic shaft member when cooling the synthetic resin to shrink.
By molding the support member with the synthetic resin around the metallic shaft member, it is possible to reduce a manufacturing cost.
With the frictional hinge device used to pivotably move a display for a portable business device, it is possible to hold the display at the desired angular positions to ensure a good view on the display.
With the synthetic resin applied to the support member in which a bending elasticity fluctuates as small as up to 30% under the operating temperature ranging from xe2x88x9220 to 80xc2x0 C., it is possible to maintain a sufficient surface friction resistance against the metallic shaft member even when the normal ambient temperature fluctuates. This prevents deterioration of friction surfaces of the support member and the metallic shaft member so as to maintain the stable surface friction resistance for an extended period of time.
By way of illustration, the synthetic resin is represented by PC (polycarbonate), PAR (polyarylate), PPS (polyphenylene sulphide) and the like.
With the synthetic resin mixed with an organic or inorganic antifriction medium, it is possible to ensure a smooth pivotal movement with the shaft member. As opposed to the case in which greasing agent is applied between the support member and the shaft member, it is possible to prevent the perimeter from being polluted. It is also possible to exceedingly reduce the wear dust produced between the support member and the shaft member, thereby maintaining a stable surface friction resistance therebetween for an extended period of time.
By mixing the synthetic resin with fibrous material to improve its mechanical strength, it is possible to ameliorate the endurance.